1. Field of Invention
This invention relates to superconducting devices and, in particular, to a method and means for detecting normal zones in superconducting magnets or coils from a point externally of the cryostat.
2. Prior Art
Coils of a selected material made superconducting in a cryostat and the dangers of having the coils, or portions (zones) thereof, revert to their original state of resistivety, i.e., their normal state, especially rapidly (quench effect), is old and well known and there have been many devices for detecting the formation of such normal zones. For example, the coil or the cryostat have been provided with conductors (voltage taps) within the cryostat is discussed in the article "Constant Voltage Controller and Transition Monitor for Superconducting Magnets" Donald H. Lester, Journal of Applied Physics Vol 42 No. 1 January 1971 Page 80; utilization of a transformer effect to detect change in current level is disclosed in the U.S. Patent to Burnier U.S. Pat. No. 3,579,035; current decay to sense a quench through the use of a regulator in the power supply is disclosed in the German Pat. No. 213,7776; measuring the phase angle change between the supplied current and the coil voltage during a quench by utilizing a AC signal superimposed on the DC magnet current is disclosed in the French Pat. No. 2,224,909; energy supplied to a resistive loading in the cryostat is disclosed in the U.S. Patent to Halpin et al, U.S. Pat. No. 3,283,576; additional windings in the cryostat is disclosed in the U.S. Patent to R. W. Boom et al, U.S. Pat. No. 3,176,195; the use of an accoustic wave is disclosed in the U.S. Patent to Nomura et al, U.S. Pat. No. 4,140,02; and many others.
None of the prior art detection systems however, utilize the concept of monitoring and comparing energy consumption per unit time to detect the quench mechanism of a superconducting coil. These systems also require additional coils, voltage taps, additional windings on the superconducting coil itself or in the cryostat, which impact on coil or cryostat fabrication cost.
Accordingly, it is an object of this invention to detect propagating normal zones in the superconducting coils or magnets by monitoring the energy consumed by the coil or magnet per unit time and comparing that value with a previously recorded or stored value of energy consumed per unit time.
A second and equally important object of this invention is to monitor the energy consumed by the coil/magnet from outside the cryostat thus eliminating the need for voltage taps and interface requirements between the cryostat and the ambient temperature environment.
Still another object to this invention is to provide external quench detection circuitry for carrying out the foregoing method and to reduce the amount of hardware that is needed to detect normal zone formation in superconducting systems.